Leptospirosis among rice mill workers of Salem, South India

Leptospirosis is not commonly reported from the Salem district in central Tamil Nadu in India. In October 2000, a rice mill worker, who had fever and jaundice, tested positive in leptospiral IgM enzyme-linked immunosorbent assay (ELISA). Microbiological and serological investigations were performed on the patient, a sample population of the rice mill workers, and the animal and rodent populations living in the same premises. Leptospira was isolated from the patient about 2 weeks after the onset of symptoms when he had recovered from illness following a course of doxycycline. The isolate was serovar Icterohaemorrhagiae of serogroup Icterohaemorrhagiae. The patient also showed a fourfold rise in titers in microscopic agglutination test (MAT) and IgG ELISA. The rice mill workers had a seroprevalence rate of 68.3%, which was significantly higher than that among a control group consisting of persons engaged in other occupations. Serological studies conducted among cattle, dogs, cats, and rats showed seroprevalence rates of 52.9%, 50.0%, 66.6%, and 52.1%, respectively. Leptospires were isolated from two rats, but the isolates were lost during subculturing and could not be characterized. The most predominant serogroup identified by MAT was Autumnalis for rice mill workers and all animal populations. The other serogroups that reacted in MAT were Icterohaemorrhagiae, Australis, Grippotyphosa, and Patoc. Although Australis and Grippotyphosa showed agglutination in the case of human samples, none of the animals had detectable titers to these serogroups. The rice mills of Salem, having large rodent populations, various animals living in close proximity, a wet environment, and unprotected exposure of the workers to the environment, constitutes an ideal setting for transmission of leptospirosis and could be an epidemiological niche of leptospirosis.